Because of apparent reproductive isolation between Northern and Southern hemisphere populations of the black drum Pogonius cromis, we tested the hypothesis that advertisement calls from a southern population would differ from known calls of North American populations. Additionally, we quantified disturbance and advertisement calls, their changes with fish size and sex, not previously examined in this species. Unlike most sciaenids, both sexes of P. cromis possess robust sonic muscles, and both produce disturbance calls when handled. However, only males produce an advertisement call used in courtship. The disturbance call consists of a variable train of short-duration pulses (average 23 ms). The duration, interpulse interval, and dominant frequency of pulses are similar in males and females and change developmentally: pulse duration and interpulse interval increase and dominant frequency decreases with fish size. Advertisement calls, recorded in the field and in captivity, are long-duration (average 184 ms) and tonal. Based on variation in fundamental frequency, which decreases with fish size, field choruses are composed of different-sized individuals. The duration of advertisement calls, about a third of those from Florida populations, suggests genetic differentiation between northern and southern populations.

SUMMARY: Specimens of Rioraja agassizi were collected at Guarujá pier, São Paulo State, Brazil, from March 2005 to March 2006. A total of 275 males were captured. Based on the analysis of the clasper length, gonad weight, clasper gland length, alar thorns and lobule diameter, the size-at-maturity was estimated to be 32 cm. There were 1049 females in the record. Size-at-maturity was calculated in 40 cm. Sexual resting females were observed. Gonadosomatic and hepatosomatic indexes varied significantly in both sexes throughout the year. However, ovulation, egg-laying and presence of sperm in the seminal vesicle were observed all year round. For this reason, an annual cycle with at least one peak in the sexual activity is proposed for this species. De acuerdo con el análisis de la longitud del clasper y de la glándula del clasper, el peso de las gónadas, el diámetro de los lóbu-los y el número de espinas alares, el tamaño de primera madurez sexual fue estimado en 32 cm. Se capturó un número de 1049 hembras. El tamaño de primera madurez sexual fue calculado en 40 cm. Se observó reposo sexual en hembras de esta especie. Los índices gonadosomáticos y hepatosomáticos variaron significativamente en ambos sexos a lo largo del año. Sin embargo, la ovulación y la deposición de cápsulas ovígeras sucedieron continuamente durante todo el año, así como la presencia de esperma en la vesícula seminal en ejemplares adultos. Por este motivo, se propone para esta especie, un ciclo reproductivo anual, con por lo menos un pico en la actividad sexual. KeywordsPalabras clave: clasper, elasmobranquios, glándula nidamentária, deposición de cápsulas ovígeras, gónadas. and hatch. Oviparity in skates is single (external) (Musick and Ellis, 2005) and all Rajids have the same general reproductive cycle, in which egg capsules are deposited in pairs with intervals of 0-5 days between successive depositions (Holden et al., 1971). In the wild, there is a peak in egg laying during the summer and spawning occurs throughout the entire year (Clark, 1922).The Rio skate Rioraja agassizi Whitley, 1939 (Rajidae: Arhynchobatidae) is endemic to the southwestern Atlantic coast of South America (Compagno, 2005) and occurs from coastal waters to depths of up to 130 m (Figueiredo, 1977). Females deposit egg capsules with mean dimensions of 47x31 mm (Oddone et al., 2006). Apart from the description of the egg capsule, the reproductive biology of R. agassizi-i.e. its sexual development, size-at-maturity and cycle-is unknown.The assessment of chondrichthyan populations requires a quantitative approach to the study of reproductive biology, size-at-maturity being a key parameter to be estimated (Walker, 2005). In addition, over the past thirty years, catches of rajids have increased in the western Atlantic, mainly as a bycatch of target fisheries, but sustainable catch rates are completely unknown (Frisk et al., 2002). Thus, knowledge of the reproductive parameters, in particularly size-at-maturity, is especially important for making decisions on stock management. I...

The whitemouth croaker produces two different sounds using extrinsic sonic muscles: (1) male advertisement calls during the spawning season and (2) disturbance calls, produced by both sexes. The advertisement call, related to courtship, was recorded in the field and from two marked spawning males of 28 and 30.5 cm L T in the laboratory. It consists of individual pulses with average durations of 19.7 ms and 17.8 ms for the two males respectively, interpulse intervals of 496 ms and 718 ms, and dominant frequencies of 280 Hz and 316 Hz. Pulses are emitted in bouts of one to three min duration. Disturbance calls consist of a burst of pulses produced at short intervals, and the pulse duration, interpulse interval and dominant frequency of the pulses average 19.8 ms, 17.1 ms, and 363 Hz, respectively. Dominant frequency and interpulse interval decrease and pulse duration increases with fish size. Sound characteristics change markedly in young of the year individuals (lower than 25 cm L T ) after which they appear to stabilize. Higher dominant frequency in the advertisement than in the disturbance call and the relationship of dominant frequency to pulse duration suggest that dominant frequency is determined as a forced response to muscle contraction parameters rather than by the natural frequency of the swimbladder.

The population structure and reproductive biology of Mustelus schmitti was analysed during autumn (1994, 1995) and spring (1994) in the Rio de la Plata oceanic front. The samples consisted mainly of adult males and immature females, indicating that nursery areas are situated elsewhere. In autumn, the highest female densities occurred between 368S and 358S, with densities decreasing further south, and high male densities occurred over all latitudes of the study area. In spring, both sexes occurred north of latitude 36830 0 S. Males attained maturity at 59 cm total length (TL), and females at 72 cm TL. Litter size varied from one to ten in spring and two to nine in autumn, with embryos ranging from 9 to 26 cm and 7 to 26 cm TL respectively. The mean TL of embryos was signi¢cantly higher in spring (22 cm), suggesting that parturition occurs in late spring and summer. Litter size was found to increase with female TL.